I agree they all taste pretty much the same when they are cold, most tap water included.

However not all tap water is equal. The source of the tap water here was recently changed from mountain resovoirs in Wales to local bore holes and the taste has gone from pretty great to just about OK. However if you leave it to stand overnight it is just horrible by the morning, something the old source never suffered from.

Apparently sales of bottled water went up significantly in this area when the made the change.